I found another company, Terremark (which Verizon recently announced they intend to buy), that offers a cloud computing service called vCloud Express. They're based on VMware, so it is possible to run several flavors of BSD on it (including OpenBSD, although it's not officially supported. There's no IPv6 support, and it's 0.037 US$/hour. I haven't tried it out yet, but will consider it if I decide I need public OpenBSD cycles again.